1. Field of the Invention
The present invention relates to an axial plain bearing assembly and in particular, to an axial plain bearing assembly suitable for the axial support of the drive shaft of a combustion air-charge compressor for use in internal combustion engines.
2. Background of the Related Art
For the axial support and sealing of the drive shaft of a turbo-mechanically driven centrifugal or screw-type compressor or a turbo compressor having an exhaust-gas driven turbine, the special operating conditions of such aggregates require appropriate attention. For instance the drive shafts generally have a very small diameter that is frequently substantially less than 40 mm, and, at the same time, these shafts are rotated at very high rotational speeds of e.g. 105 min−1 and more.
The seal of such compressors can be subjected to both over pressure and low pressure conditions prevailing in the interior of the compressor casing. Therefore it should be ensured that the gaseous medium requiring sealing, which is usually air, be kept free as far as possible of non-gaseous components such as oil particles since oily residues would otherwise enter the combustion chamber of an internal combustion engine thereby having an environmental impact (the production of plumes of smoke from the exhaust) apart from affecting the operational behaviour of the internal combustion engine. Hitherto, labyrinth seals or a sealing effect produced by means of piston rings were mostly used, both of which are associated with a relatively high degree of leakage. Also mechanical face seal assemblies (e.g., those described in EP-A-1 054 196) have already been installed because of their substantially smaller degree of leakage, whereby care must be taken to prevent dry-running.
Plain bearings are generally preferred for the radial and axial support of the drive shaft. The separate structural measures for the sealing and bearing functions involve an increase in the structural parts and assembly costs for fulfilling the functions of supporting and sealing. On the other hand charge compressors of the present type are typically mass-produced and should be suitable for automatic handling in motor vehicle production lines. This requirement can be taken into account all the more easily, the smaller the number of parts that have to be handled and assembled.
The conventional methods and systems generally have been considered satisfactory for their intended purpose. However, there remains a need in the art for a method and system providing improved axial support and sealing of a shaft, particularly in the driving shaft of a compressor. There also remains a need in the art for such a system and method that have low part counts, and are easy and inexpensive to make and use. The present invention provides a solution for these problems.